Pigment preparations are combinations of pigments with pigment dispersants that are structurally analogous to pigments and are substituted by groups having a specific activity. They are added to the pigments in order to facilitate dispersion in the application media, especially in varnishes, and to improve the rheological and coloristic properties of the pigments. The viscosity of the highly pigmented paint concentrates (millbase) is lowered and the flocculation of the pigment particles is lessened. By this means it is possible, for example, to increase the transparency, which is desirable especially in the case of metallic pigments.
A large number of proposals exist for improving the rheological and coloristic properties of organic pigments by adding pigment dispersants, although not always with the desired result.
EP-B-0 321 919 describes the preparation of pigment preparations by mixing the base pigments with pigment derivatives that contain methyleneimidazolyl groups. In the field of perylene pigments, this results in pigment preparations whose coloristic properties no longer meet current requirements.
DE-A-3 106 906 describes the preparation of pigment dispersants that contain sulfonamide groups. The pigment dispersants described therein are based on perylene compounds but have considerable coloristic and rheological deficiencies.
U.S. Pat. No. 4,762,569 describes the preparation of pigment preparations on the basis of symmetrical perylene-3,4,9,10-tetracarboxylic diimides. These pigment preparations are suitable only for use in solventborne systems. They do not meet all of the requirements in terms of rheological and coloristic properties that are made of pigment preparations. At high pigment dispersant contents in particular the coloristic properties are no longer adequate and in many cases a distinct loss of gloss and marked shade deviation can be noted. Furthermore, these pigment dispersants possess inadequate solvent fastness and fastness to overcoating, thus greatly restricting their universal application. Moreover, in many varnish systems it is possible to observe instances of incompatibility with the binder, which is prohibitive for their use.